Experimental study and numerical simulation with a coupled CFD–PBM model of the effect of liquid viscosity in a bubble column

• Influence of liquid viscosity on the hydrodynamics in a bubble column was studied.
• Volume fractions of both large and small bubbles were determined by DGD method.
• Numerical simulations were carried out with a coupled CFD–PBM model.
• Coupled CFD–PBM model successfully predicted the effect of liquid viscosity.

The effect of liquid viscosity on the hydrodynamic behavior in a bubble column was investigated by experimental study and numerical simulation with a coupled CFD–PBM (population balance model) model. The total gas holdup and volume fractions of small and large bubbles were determined by the dynamic gas disengagement method. In the low viscosity range, the total gas holdup and the volume fractions of small and large bubbles were almost independent of the liquid viscosity. In the high viscosity range, an increased viscosity gave a decrease in the total gas holdup and volume fraction of small bubbles and an increase in the volume fraction of large bubbles. The simulation captured these features and showed that when the liquid viscosity was <10 mPa s, the viscosity had negligible effect on the bubble breakup rate and daughter bubble size distribution, while a further increase of the liquid viscosity significantly decreased the bubble breakup rate and increased the probability of equal breakup. The influence of liquid viscosity on bubble coalescence was less important than its effect on bubble breakup for the hydrodynamic behavior. With the use of the multiple bubble breakup and coalescence models and the use of the bubble size distribution to describe the interphase forces, the coupled CFD–PBM model could describe the dependences of the total gas holdup and volume fractions of small and large bubbles on liquid viscosity in both the homogeneous and heterogeneous regimes.